Planting and growing a strategic mix of cover crops
not only reduces the loss of nitrogen from farm fields protecting water quality in the Chesapeake Bay, but the practice contributes nitrogen to subsequent cash crops improving its yields.
A. reduces the loss of nitrogen from
farm fields protecting water quality in the Chesapeake Bay,
but the practice contributes nitrogen to subsequent cash crops improving its yields.
B.
reducing the loss of nitrogen from farm fields, protecting water quality in the Chesapeake Bay,
and the practice contributes nitrogen to subsequent cash crops improving its yields.
C. reduced the loss of nitrogen from farm fields and protected water quality in the Chesapeake Bay,
and the practice contributes nitrogen to subsequent cash crops, improving their yields.
D. reduces the loss of nitrogen from
farm fields, protecting water quality in the Chesapeake Bay,
but the practice
also contributes nitrogen to subsequent cash crops, improving their yields.
E.
reducing the loss of nitrogen from farm fields, protecting water quality in the Chesapeake Bay, but the practice contributes nitrogen to subsequent cash crops improving their yields.
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Option D is the answer because it is the only option that follows the idiom "not only X but also Y".
Also good to note that in option A, "protecting" is modifying "farm fields", whereas in option B it is modifying "Planting and Growing".